This app is a subnet calculator for iPhone.
"network address", "host address", "number of host addresses" and "directed broadcast address" are shown when you enter an IP address and a prefix.
You can see the subnet mask when you set a prefix (bits length of network number portion) on this App. Reversely, you can see the prefix when you set a subnet mask.
Class of the IP address and "NAME" of "Special-Purpose" are shown for the entered IP address. ("Special-Purpose" is shown based on the RFC 6890(April 2013) )
This app supports classless addressing.
For instance, this app allows to set 8 bits prefix for a class B address when it is in classless mode.
This App could be used for education purpose of IP address.
Would you use this app for learning of network behavior, network equipment (router , L3 switch , etc) , Professional certification (CCNA etc) ?